1. Field of the Invention
The present invention relates to mutant liquefying alkaline α-amylases which have excellent heat resistance, and are particularly useful as enzymes for detergents, and genes thereof.
2. Description of the Background Art
When an α-amylase [EC.3.2.1.1] is used as an enzyme for detergents, it has heretofore been said that a liquefying alkaline α-amylase, which can decompose starch at random and is stable to alkali and also to both chelating component and oxidation bleaching component, is preferred. However, in liquefying amylases, a calcium ion is generally important for maintaining the structure of the enzymes, and the stability thereof is lowered in the presence of a chelating agent. Besides, most of such enzymes have had the optimum pH in a neutral to weakly acidic range.
Under the foregoing circumstances, the present inventors found that enzymes produced by alkaliphilic Bacillus sp. KSM-K38 (FERM BP-6946) and Bacillus sp. KSM-K36 (FERM BP-6945) strains isolated from soil do not show the lowering of activity at all in the presence of a chelating agent at a high concentration by which deactivation is recognized in the conventional liquefying α-amylases, and have resistance to surfactants and oxidizing agents and that they have higher activity on the alkaline side compared with the conventional liquefying α-amylases and are useful as enzymes for detergents (Japanese Patent Application No. 362487/1998.
However, said enzymes exhibit inactivation at a temperature of 50° C. or higher, and so the heat resistance thereof have been somewhat insufficient in view of the fact that cleaning of clothing and tableware is generally conducted at about 10 to 60° C.